Reactance tube controlled generator



June 17, v1947. N. 1. KORMAN REACTANCE TUBE CONTROLLED GENERATOR Filed Afig. 31, 1942 2 Sheets-Sheet IIIL INVENTOR NA THAN/EL f lfofiMAzv.

ATTORNEY Patented June 17, 1947 'REACTAN TUBE CONTROLLED GENERATOR Nathaniel .I. Korman, Camden, N. J assign'orlto Radio Corporation of America, a corporation of Delaware Application August 31, 1942, Serial No. 456,730

22 Claims. 1,

-';lh-is application concerns a new and improved system for controlling the angular velocity of wave energy in accordance with control potentials, such as, signals or potentials used for automatic frequency control purposes. In-my system, I employ reactance tubes in anew and improved circuit arrangement wherein oscillations are generated and modulated in phase, or in frequency, 'or-contro'lled as to phase or frequency in accordance with'controlpotentials of any nature. In the specification and claims the term wave length modulation will be used and it will be understood that the same means phase and frequency, as well as phase or frequency modulation.

The problem of'providing a frequency modulation exciter for broadcast service is complicated by two conflicting requirements, stability of the carrier, and adequate frequency swing with low distortion. The Federal Communications Commission has specified that the carrier, in the 42-50 mo. band must have a stability better than 152.000 C. P. S. and a frequency swing of '75 kc. with an overall microphone-to-antenna distortion of less than 2%. Y

Commercial .exciter units have been of two types, phase modulators and frequency modulators. Phase modulators, because the carrier frequency is determined by piezo-electric crystals, can easily be made to have the required stability, but inherently are low-level modulators requiring several thousand times multiplication before adequate frequency swing is obtained. The high multiplication requires many tubes and brings abouta troublesome noise problem which necessitates comprising between too much distortion and too much noise. Phase modulator types of exciters have not proven very satisfactory because of the high noise, high distortion, and complication of many stages of multiplication.

Frequency modulators, comprised of reactancetube-modulated self-excited oscillators usually have quite low distortion and noise but are inherently unstable in carrier frequency. The carrier frequency may be stabilized by some form of automatic frequency control. This expedient has been used in all commercial exciters of the frequency-modulator type and has proven successful. The main objections have been the complexity of the equipment and, in some cases, that adequate stability,even with automatic frequency control, is difiicult :to obtain.

A'pr-imaryobject of my invention is to provide a wave length -modulation system which will satisfy the. above requirements with respect ta 2 irequency drift, low distortion, etc -wit-hout'the use of automatic frequency control circuits.

In describing thy-invention reference will be made to the attached-drawings,wherein Figure l is a basic wiring diagramof an oscillator and a reactance tube control therefor arranged in accordance with my invention.

Figure 2 is a vectordiagram showingthe phase relation of the various voltages appearing in the circuit of Figures 11, 3 and 4.

Figure 3 is a more complete diagram, of a controlled oscillator of the nature shown in Figure 1.

Figure 4 illustrates somewhat completely an angular velocity of wave length modulationsystem arranged in accordance with my invention and including features of Figures 1 and 3 and additional improvements which work to increase the stability of my system. Figure 4 is a somewhat complete diagram of a modulated oscillator which operated Well within the requirements outlined above.

The. frequency drift of. a reactance tube frequency modulator with plate andscreen voltage changes may be analyzed. into four factors: 1. Oscillator tube transconductance change; 2. Oscillator plate resistance change; 3. Reactance tubeiplate resistance change; 4. Reactance tube transconductance change. In general the magnitude and-direction of the frequency drift due to these changes will depend on the circuit being used. A stabilized unit can be provided by ad,- justing the frequency drifts due to, one or=more of the four factors so that the total frequency drift is made very small.

Consider, now, the effect of the reactance tube onv the oscillator. If the reactance tube grid voltage is exactly in quadrature with the reactance tube plate voltage. (this is the same as the oscillator tankvoltage, usually), then the reactance tube will appear to the oscillator tank circuit as a pure reactance shun-ted by the plate resistance of the reactance tube. If, on the other hand, the reactance tube grid voltage ismore than out of phase with the plate voltage, the reactance tube will appear'to theoscillator tank a reactance and a resistance equal to the plate resistance, and also anegativeresistance, all in parallel. The magnitude of this negative resistancewill dependon the phase angle mentioned above. if the phase is less than 90,the negative resistance becomes a positive resistance.

the adjustment of the phase angle, between the reactance tube grid voltage and'the plate. yoltage enables us to. regulate the sizeiof I condensers, etc. have been omitted from this fig-i ure).

In Figure 1, 20 is the oscillator tube. Tubes 30 and 50 are the reactance tubes. The oscillator has a tank circuit comprising capacitor CI and inductance Ll coupling its anode and control grid in a regenerative circuit. The anodes of the reactance tubes 30 and 50 are tied together and connected to the oscillator tube anode end of tank circuit Cl-Ll. The cathodes of the reactance tubes 30 and 50 are tied together and to the cathode of the oscillator tube 20 and to a point on the tank circuit inductance Ll. The control grids of the reactance tubes are coupled in push-pull relation by a phasing tank circuit including inductance L2 and condenser 02. The inductance L2 is inductively coupled to the inductance LI and the electrical center 2 of L2 is connected by a movable tap to a point on LI.

.The generated voltage on the tank circuit between the points 1 and 0 (the cathodes of tubes 30 and 50 are also connected to this point) is represented by el 0 in Figure 2, and since the anodes of the reactance tubes 30 and 50 are tied together, this voltagemay also be considered as being applied to the anodes of reactance tubes 30 and 50. The voltage between the point 0 on LI and the point 2 on'L2 is represented by the vecto e02 in Figure 2-, and, obviously, this voltage being tapped from a point on LI on the other side of the point 0 with respect to point 1 is 180 out of phase with respect to the voltage represented by ell]. A voltage is induced from Ll to L2 and appears across L2. This voltage between the points 2 and 3 is represented by the vector e23 in Figure 2 and the voltage between the points2 and 4 is represented by the vector e24. Note that these vectors also may be considered as representing the voltages applied differentially to the control grids in the absence of the movable tap connection between LI and L2 which forms a part of my improved system and introduces the voltage represented by vector e02. The voltage between the points 0 and 4 is represented by e04 and this also represents the voltage on the grid of reactance tube 59. The vector e03 represents the voltage between the points 0 and 3 and also represents the generated voltage on the grid of tube 30. The vector e04 is a resultant of vectors e02 and 624, while the vector e03 is a, resultant of the vectors e02 and e23. In the position shown vector e02 represents a'voltage in phase opposition to the voltage represented by vector ell] and the phase angle 0 is more than 90 so that the tube reactances are complex and include a negative resistance component as well as a reactive component. By adjusting this tap, the resultant voltage set up on the control grids of the reactance tubes 30 and 50 may be adjusted to have 90 displacement relative to voltages on the anodes of tubes 30 and 50 or more than 90 or less than 90. a a

By moving the tap up on inductances LI past point 0, this phase angle may be made less than 90 to provide positive resistive components.

part at least of the tank circuit, Cl-'-Lll.

As explained in columns 2 and 3, adjustment of shown in more detail a tube generator with a pair of tube modulators connected thereto and in so doing reference letters and numerals corresponding to those in Figure 1 are used. In Figure 3 I have shown the biasing circuits for the oscillator tube 20 comprising a choking inductance L4 and biasing resistor RI. The oscillator circuit also includes a blocking condenser C3 and there is a second blocking condenser CI in the connection between the points on LI and L2 and a potential source bypassing condenser C4. The reactance tube tank circuit L2-C2 is coupled to the grids of reactance tubes 30 and 50- by blockin and coupling condensers C6 and C8. In Figure 3, the reactive effect with or without a resistive component, which may be negative or positive, is obtained as disclosed hereinbefore. effect may be controlled by applying modulation voltages differentially between the control grids of the reactance tubes by way of radio frequency choking inductances L3. Bias for the reactance tubes is also supplied to these leads. This bias may be supplied to the center tap of a biasing ings. In Figure 4 the oscillator comprises a tube V 20 having its anode and control grid regeneratively coupled by a tank circuit comprising inductance C lLl. The anode connection includes a plate supply voltage dropping means 2| comprising a resistance and condenser in parallel. The tube, as arranged and coupled, operates in a well known manner to produce sustained oscillations which appear in the tank circuit. The electrode supply potential connections have been shown somewhat completely in the drawings and will not be described herein.

The modulating reactance tubes 39 and .50 have their anodes tied together and connected by lead 32 to the anode end of tank circuit Cl,-,-Ll. The cathodes 3d and 5 of the reactance tubes are connected to ground for oscillations of the generated frequency by condensers 52 and 52 so that the impedances between the output electrodes of tubes 30 and 50 are in parallel with a control grids of the reactance tubes 30 and .55 are connected in push-pull by a phasing tank circuit comprising split inductances L2 shunted by adjustable tuning condensers C2. Condensers 39 and 39 are bypass condensers which do not impede the flow of radio frequencies but which do prevent inductances L2 and L5 from shorting the audio transformer 48.

The electrical center of the condenser system is connected to ground and by damping resistors R3 to the cathodes of. the tubes through coupling and bypassing condensers C5. V

The inductances L2 are, as stated above, in two sections and include in the connectiontherebetween an inductance L5 inductivelycoupled'to LI. This inductance L5v picks up generated vo t ge and supplies them substantially differ- The reactive The J entially to the control-grids of tubes 30 and 50.

The control grids of reactance-tubes and 50 are also difierentially coupled to 1 the split secondary windingscf a transformer --4'0. The couplings between secondary windings of transformer 4B and the control grids "of-the reactance tube include high frequency choking 'inductances L3 and the secondary windings are-shunted by a radio frequency bypass condenser 43. Adjacent terminals of the secondary windings of the transformer '40 are connected to:the respective reactance tube cathodes by way of the coupling-and blocking condensers C5, which are ot sufiicient size to pass-readily potentials of control or modulation frequency. The screen grids of reactance tubes 30 and 50 are connected 'to the supply sources by circuits including filter networks as are the control grids and anodes.

Bias'for the control grids is derived' by adjustable biasing resistors -56 and 56. These bias circuits are completed by way of resistor =51: and groundand from ground to resistors R3 and resistors 58 and 58 to the control grids of the two reactance tubes. Note that since the control'grids are connected to the end of the cathode resistors remote from the cathodes and sincein this bias circuit potentials of modulation frequency are shunted by 05, direct current degeneration is obtained for reasons pointedout hereinafter.

' As will be understood 'frorn the foregoing description, the-generated voltages on the reactance tubes anodes are of like phasawhile the reactance tubes control grid voltages are of substantially'opposed phase with one tubes grid voltage advanced substantially 90 with respect to that tubes anode voltage and the other grid voltage retarded "substantially 90 with respect to the latter tubes anode voltage. One tube, as a consequence, reflects or adds to thetank circuit C ILI and inductive reactance component, while the other tube adds'thereto a capacitive reactance component so that differential modulation of the tubes changes the tuning of the tank circuit and. as a consequencethetuning of the-tank circuit is controlled by the modulation potentials" from source 60.

Since the modulationis differential. ingeneral itmay be-state'dthat variations in electrode potential. which are in phase, cancel out, while differential variations in accordance with control potential aid each other in their effect .on the reactance reflected into the tank circuit.

In the system, instability of the oscillator due to changes in the' oscillator tube Etlfl' minimized by the use of a large-oscillator tank c'apacitance at Cl. However, the size of-thiscapacitor is limited by the frequency swing required and the amount of reactive current available from the reactance tubes. Push-pull reactance tubes are used to permit the use of a larger oscillator tank capacitor and to balance out the efiects on frequency'drift due to supply voltage changes. To minimize frequency drift due to variations in the input circuit of the apparatus to be driven by this oscillation,- the outputis taken by lead 6| from the grid circuit of tube 25. and it is intended that theinput circuit of the driven apparatus at 10 be the grid of a tube operated in Class A.

A serious 'cause'of drift in'reactance tube os cillators arises from changes in contact-potentie] between cathode and grid of 'the reactance tube. 'I'he-contactpotential is of the order'of -0.7 volt and varies erratically zwith ';life.and

heater voltageover a range of several tenths vof. .:a

is undesirable because it has the same phase 'F; C Cfrequirements call for a ratio of dri-ft'to useful frequency swing to be less than Evidently, the effect of .these contact potential variations must be reducedconsiderably if the drift requirements are to be met.

In system direct .current degeneration .is usedto reduce the eifectv of changes in contact potential. The cathode resistors 56 .and.56' are made large inorderto obtain the. desired amount of degeneration. fWhere tubes of 1614 type were used at 3lland 50 .inorder to-obtain a degenera- .tion. of ten times, a cathode resistor of. 1800 ohms .isnecessary. The direct, currentdrop across these resistors willbe volts. It is, therefore, necessarytoobtai-n the .correct control grid bias from avoltage divider 51 in the. power supply.

Degeneration in the reactance tube circuits. at audio .frequencies must .be avoided because its 'efiect. is to destroy the linearity of the transconductance .vs. grid biasncharacteristicand to introduce distortion. Such degeneration at the audio frequency or. modulation potential frecuencyiskeptdown to asufliciently smalldegree by use of the audio voltage input directly from .cathode to grid of each. reactance tube as. shown.

It is also necessaryin .this connection to prevent an. audio voltage from developing between cathode andscreen grid. This is accomplished by .usingdarge capacitors 59 in the screen .gridto cathode circuits.

An. important cause of frequency drift in oscillators is-due-. to the change of inductance and capacitancein. the tank circuit with temperature variations and I include the tankcircuit in a chamber 3|, which is temperature controlled .by

means shown.- Thetank circuit is also shielded to prevent reaction thereon from the phase adjusting circuits L2-C2 except as desiredand obtained by couplings thereto.

' As explained previously, theefiects of contact potential changes in. the reactance tubes are minimized by the use ofdegeneration. The efiects tubes are minimized bythe push-pull connection.

of changes in transconductance of the reactance A meter MA andvar-iable resistors are incorporated-in the. circuit between points A l and A--2 for indicating and readjusting this balance.

It has been-noted experimentally that a sizeable -=quadrature grid voltage appears on the reactance tubes eventhough the pickup coil for the .phasin circuitis disconnected. This voltageappears on the grid because of residual plateto-grid capacitance in the reactance tube .and

onboth reactance tube grids (for push-pull operation,'the-reactanc.e tube grid voltage must be out of phase with each other) and results inninequalitiesin'the radio-frequency voltages. on the reactance tube grids. I p

. It. ispf; extreme importance that the radio-frequency; voltage on the gridsof the tworeactance tubes be equal. To assure this, I have found it necessaryto neutralize the reactance tubes because the unneutralized plate-to-grid capacitance causes a serious unbalance of the reactance tubes and, consequently, a large frequency drift with plate supply voltage change. The neutralizing condensers are shown at NC and are connected between the control grid of the reactance tubes 30 and 50 and the control grid of the oscillator 20. These neutralizing condensers feed from the grid of tube 20 to the grids of tubes 30 and 50 voltages substantially equal to the voltages fed from the anodes of tubes 30 and 50 throughthe tubes to the control grids. The voltages fed to the grids are of opposed phase and thereby neutralize each other.

.The function of the grid-phasing circuit L2- '02 is to couple from the oscillator tank to the grids of the reactance tubes in such a way as to make the, voltages on the grids of the reactance tubes equal, and approximately 90 out of phase with the voltage across the oscillator tank, one leading phase and the other lagging.

If the (quadrature components of the) reactance tubegrid voltages are not equal, the reactance tube blance willlbe destroyed and plate supply voltage changes will cause a comparatively large frequency shift. If the reactance tube grid voltages are not exactly 90 out of phase with the oscillatortank voltage, the effect will be to introduce a negative. (or a positive, depending on the :phasing) resistance component into the reactance tube plate currents. This resistive component of reactance tube plate current will vary with modulation and cause amplitude modulation. A moderate amount of negative resistance due to the phasing is desirable since its manner of variation with modulation will be correct to cancel 'the effect of plate resistance of the reactance tube which alsovaries with modulation.

When the phasing tank capacitors C2 are correctly tuned, the reactance tube grid voltages are maximum and exactly 90 out of phase with the oscillator tank voltage. When the phasing is .tuned correctly, it has been found that minimum distortion is obtained. Also the amplitude modulation, as observed on a cathode ray oscilloscope,

is mostly second harmonic and contains no fundamental component. The minimum distortion criterion of tuning is not a critical one but the amplitudemodulation criterion is quite sensitive to slight detuning. It has been found that when the phasing tank is detuned far from resonance, the resistive component of reactance tube plate current may be sufficient to throw the circuit out of oscillation over part or all of the modulation cycle. For other conditions of extreme detuning,

the negative resistance component of reactance tube plate current may predominate and increase the amplitude of oscillation enough to overload the reactance tube grids with radio frequency voltage and thus cause severe distortion when f modulation is attempted. It will be noted that a shield, 31, has been placed between the oscillator tank andthe pickup coil. This shielding has been found to be quite important. Capacity coupling {from oscillator tank to the pickup coil results in quadrature and resistive components of reactance tube grid voltages which have the same phase on "both the grids. The results of such capacity coupling are amplitude modulation which may be severe enough to put the circuit out of oscillation during part or all of the 'modulation cycle and an unbalance of the reactance tubes which allows plate supply voltage changes to cause frequency drift, p A moderate amount of amplitude'm'odulation is not serious succeeding class C amplifier stages in the transmitter are effective in removing it. However, as has been stated before, a tendency to excessive amplitude modulation can overload the grid of the reactance tubes and also may put the circuit out of oscillation for part of the mod: ulation cycle, I v

In the modifications illustratedin Figures land 3 a'connection is supplied between the electrical center of inductance L2 and a point on the inductance Ll to supply the voltage represented by the vector e112 (Figure 2) to thereby introduce the'more than or less than phase quadrature relation between the generated voltages .on the grids and anodes of tubes 30 and 50. In some cases the connection shown in Figures 1; and-3 is necessary to provide this voltage. In other cases, such as, for example, .the modulator illustrated in Figure 4, stray capacitance between L5 and LI accomplishes the same result, and the di-.

rect connection is not desirable or necessary- The polarity of the voltage represented by vector e02 can bemade to oppose the voltage represented by vector ell] asshown in Figure 2, or to be the same as that of the voltage represented by ell] depending on the point on coil Li at which the stray capacity originates.

If the stray capacitance is predominantly from the bottom of LI the resistance'component will be negative. If the stray capacitance is predominantly from the top of LI the resistive component'willbe positive. Thus, by adjusting the position of L5'with respect to LI the sign of the resistive component introduced into the oscillator tank may be controlled.

I claim:

1. A simulated reactance comprising twoelectron discharge systems each having an electron receiving electrode, an electron flow control electrode, and an electron emission electrode, an inductive reactance across which alternating voltages appear, connections tying the electron receivin electrodes together and to a terminal of ages, connected between said flow control elec- I trodes, a coupling between said inductances whereby voltages of a secondphase are set up in phase opposition on-said electron flow control electrodes, and means for supplying a third voltageof reversible phase and adjustable amplitude in phaseto said flowcontrol electrodes tothereby modify the phase of said voltages of saidsecond phase. i j

2. In a signalling system, a tube generator having electrodes regeneratively connected in an oscillation generating circuit, a reactance tube having two'electrodes coupled to the generator toderive therefrom voltages of the generated frequency substantially in phase quadrature whereby a reactive effect is'provided in said-reactance tube, connections between the reactance tube and 3. In apparatus of thenature described, apair ofaelectron discharge tubes each having an. anode,

sh me a cathode, and a control grid, a reactance comprising an inductance, the tuning of which is to be controlled, a connection between one terminal of said inductance and the anodes of both of said tubes, a connection between a point on said inductance and the cathodes of both of said tubes, a pair of inductances in series between the control grids of said tubes, a coupling between said series inductances and said first mentioned inductance, two condensers in series in shunt to said pair of inductances, a connection between adjacent terminals of said condensers and the cathodes o1 saidtubes, and means for impressing control potentials differentially on said control electrodes.

4. In a wave length modulating system, an oscillation generator comprising an electron discharge tube having an anode, a cathode, and a control grid connected in an oscillation generating circuit including atuned inductance enclosed in a shield member, a pair of electron discharge devices each having an anode, a cathode, and a control grid, 2, connection tying the anodes of said devices together and to a terminal of said inductance, a connection betwen the cathodes of said devices and a point on said inductance, a circuit comprising an inductance tuned to the frequency of the oscillations generated coupling the control grids of, said devices inpush-pull relation, a coupling between said last-named inductance and said first-named inductance, an electro-static shield in: the coupling between said inductances, and means for differentially modulating the discharge devices in accordance with signals.

5, In a wave length modulation system, an oscillationgenerator comprising an electron discharge tube having an anode, a cathode and a control grid connected in an oscillation generating circuit including a tuned inductance enclosed in a shield member, a pair of electron discharge devices each having an anode, a cathode,-anda control grid, a connection tying the anodes of said devices together and to a terminal of said inductance, a connection between the cathodes of said devices and a point on said inductance, a circuit comprising an inductance tuned to the frequency of the oscillations generated coupling the controlgrids of said devices in push-pull relation, a coupling between said last-named inductance and said first-named inductance, an electro-static shield in the coupling between said inductances; a neutralizing condenser connecting the control grid of each of said devices to said generatonand meansfbr differentially modulating the discharge devices in accordance with signals.

6. In apparatus of the nature described, an electron discharge system having an electron receiving electrode, an electron flow control electrode, and an electron emission electrode, a connection for impressing alternating current voltage of a first frequency and phase on the electron receiving electrode; a connection for impressing alternating current voltage, of the same frequency and of a phase displaced substantially 90 with respect to the phase of said'voltage of said first phase on the electron 'fiow control electrode, whereby a reactive 'efiect is produced in said system between said electron-receiving electrode and said-electron emission electrode, and a coupling for'impressing-anadditional voltage of adjustable amplitude'and reversible phase on'the said electron fiow control'electrode in 'phasedisplaced relation'with respect to the said'other voltage im- 10 pressed on-said electronflow control'electrode so that the resultant voltageimpressed on said electron fiow control electrode may be displaced 90 or moreor'less with respect to the voltage on the 5 electron receiving electrode of said 7. In apparatus of the nature described, a pair of electron discharge systems each having an electronreceiving electrode, an electron flow control electrode, and an electron emission electrode, connections for impressing alternating current voltages of. like frequency and phase on the electron receiving electrodes, connections for im-,

pressing alternating current voltages of the same frequency and of opposed phase on the electron how control electrodes, said last-named voltages being displaced substantially 90 with respect to said'volt'ages on the electron receiving electrodes, whereby reactive effects are produced in said systems betweensaid electron receiving electrodes and said electron emission electrodes, and a coupling. for impressing. an additional voltage of adjustable amplitude and reversible phase on the said electron flow control electrodes in like phase and substantially in phase quadrature with respect to the'said other voltages on said electron flow control electrodes so that the resultant voltages on saidele'ctron'flow control electrodes may be displaced 90 or more or less with respect to the voltage'on the electron receivingelectrodes of said systems. a l

'8. A simulated'reactance comprising two electron discharge systems each having an electron receiving*electrode,- an electron flow control electrode, and an electron emission electrode, an inductive reactance'across which alternating voltages appear, connections tying theelectron receiving electrodes together and to a terminal ofsaid inductivereactance, a connection between a point on said reactance andthe electron emission 40 electrodes ofsaid systems, a circuit, including an inductance tuned to the frequency of said alternating voltages; connected between said flow control electrodes, a coupling between said lastnamed inductance and said first-named inductance, andhigh resistances'in the circuit of said electron emission elements and electron flow control electrodes for causing direct current degeneration'in said systems and circuits. 9IA simulated reactance comprising an elec- 59 tron discharge system having an electron receiving electrode, an electron flow control electrode, and an electron emission electrode, an inductive reactance-across which alternating voltages appear, a coupling between the electron receiving electrode and a point on said inductive reactance to setup on said electron receiving electrode a voltage oi a first phase, a coupling between a second point on said inductive reactance and the electron emission electrode of said system, 60 a coupling between said inductive reactance and saidflow control electrode for setting up thereon a voltage which is displaced in phase about 90 with respect to phase .sothat the tube simulates a reactance, and a second coupling [between a 5 point on said last named inductance and said electron-flowcontrol electrode to apply thereto a second voltage of reversible polarity and adjustable amplitude to modify the phase of the saidvoltage of secondphase, so that the same may be displaced 90 or more or less with respect to said voltageof' first phase to include in said simulated reactance a resistive component of' adjustable amplitude-and reversible phase.

10. In 'asignallingsystem', a tube generator having electrodes regeneratively connected in an the generator to derive rature whereby a reactive effect is provided in said reactance tube, connections between the reactance tube and the generating circuit to add said reactive effect to said circuit to determine in part the frequency of the oscillations generated, a source of direct current potential and circuits including contacts coupling the same to electrodes in said reactance tube and means for reducing the efiect of changes in contact potential on the frequency of the oscillations generated as controlled by said reactance tubetcomprising a direct current degenerative connection between said'cathode and one of said other electrodes.

11. In a signalling system, a tube generator having electrodes regeneratively connected in an oscillation generating circuit, a reactance tube having'a cathode and two electrodes including a control electrode coupled to the generator to derive therefrom voltages of the generated frequency substantially in phase quadrature whereby a reactive effect is provided in said reactance tube, connections between the reactance tube and the generating circuit to add said reactive .eiiect to said circuit to determine in part the frequency of the oscillations generated, a source of direct current potential and circuits includingpcontacts coupling the source to electrodes in said tube, an impedance degeneratively arranged in a direct current circuit between the cathode and control grid, and a voltagedivider connectedtosaid source and connected to said control electrode for supplying biasing potential thereto. V

12. In a simulated reactance, an electron discharge tube having an electron receiving electrode, an electron flow control electrode, and an electron emission electrode, a reactance across whichalternating voltage appears, a coupling between said reactance and the electron emission electrode of said tube, a coupling between the electron receiving electrode and said reactance to set up on said electron receiving electrode a voltage of a first phase, a coupling between said reactance and'said electron fiow control elec trode for setting up thereon, a voltage which is about in phase quadraturewithrespect to said voltage of said first phase so that a reactive effect is jproducedin said tube between said electron receiving electrode andsaid electron flow control electrode, and an additional coupling between said reactance and said electron flow control electrode toset up on said control electrode a second voltage'of reversible phase and adjustable amplitude to modify the phase of said voltage of second phase so that it may be displaced more than, equal to, or less than 90 withrespect to said voltage of said first phaseto provide with the said reactive efiect a resistive component of adjustable size and reversible sign. r

13.'In a simulated reactance, an electron discharge tube having an electron receiving electrode, an electron flow contro1 electrode, and an electron emission electrode, a reactance across which alternating voltage appears, a coupling between said reactance and the electron emission phase, a second coupling between said reactance:

and said electron, fiow control electrode to apply to said control; electrode a second voltage to modify the phase of said voltage of second phase so that it is displaced about 90 with respectto said voltage of said first phase, and a neutralizing reactance for neutralizing the capacity in the tube between the electron flow control electrode and the electron receiving electrode.

electrode ofsaid tube, a coupling between the 14. In a simulated controllable reactance, an

electron discharge tube having an electron -re-- ceiving electrode, an electron flow control elec-,

trode, and an electron emission electr0de, a react ance across which alternating voltage appears, a

coupling between said reactance and the electrcnv emission electrode of said system, a coupling between the electron receiving electrode and said reactance to set up on said electron receiving electrode a voltage of a first phase, a coupling between said reactance and said electron flow control electrode for setting up thereon a voltage of a second phase, a second coupling between said reactance and said electron flow control electrode to apply thereto a second voltage to modify the phase of said voltage of second phase so that it is displaced in phase more than, equal to, or less than with respect to the phase of said voltage of first phase, connections for controlling the gain of said tube in accordance with control potentials to control thevalue of said simulated'reactance, and connections including a'reactance for'neutralizing the capacity in" the tube between the electron flow control electrode and the electron receiving electrode.

15. In a simulated reactance, an electron discharge tube having-an anode electrode, a control electrode and a cathode, a reactance across which alternating voltage appears, a coupling between the cathode of said device and said reactance, a coupling between the anode electrode and said reactance to set up on said anode electrode a voltage of a first phase, a coupling between said reactance and said control'electrode to apply thereto a voltage of a second phase, a second coupling between said reactance and said control electrode to apply thereto a second voltage to modify the phase of said voltage'of second phase on said control electrode, a source of direct current potential and circuits coupling the same'to electrodes'in said tube and a high resistance in a direct current circuit between said cathode and control electrode for causing direct current degeneration in said tube and circuits.

16. In a modulation system, a simulated reactance including an electron discharge tube having an anode electrode, a control electrode and a cathode, a reactance across which alternating voltage appears, a coupling between the cathode of said device and said reactance, a coupling between the anode electrode and said reactance to set up on said anode electrode a voltage of a first phase, a coupling between said reactance and said control electrode to apply thereto a voltage of a second phase, a second coupling between said reactance and said control electrode to apply thereto a second voltage to modify the phase of said voltage of said first phase on said control electrode, a sourceof modulating potentials coupled to said tubeto control the gain in accordance with modulating poten tials, direct current biasing'circuits and a source of direct current potential connected with electrodesof said tube and a highresistance in the direct current circuit of-said cathode and control 13 electrode for causing direct current degeneration in said systems and circuits.

17. A system as recited in claim 16 wherein the coupling between said source of modulating potentials and said tube is substantially direct to reduce degeneration at the modulation frequency.

18. In a simulated reactance, a pair of electron discharge tubes each having an electron receiving electrode, an electron flow control electrode and an electron emission electrode, a reactance across which alternating voltage appears, a coupling between said reactance and the electron emission electrodes of said tubes, a coupling between the electron receiving electrodes and said reactance to set up on said electron receiving electrodes a voltage of a first phase, a coupling between said reactance and said electron flow control electrodes for setting up thereon voltages of substantially opposed phase, the voltages on each of said electron flow control electrodes being substantially in quadrature with said voltage of said first phase, a second coupling between said reactance and said electron flow control electrodes to apply to each of said control electrodes an additional voltage to modify the phase of said voltages of opposed phase so that they are displaced in phase more than, equal to, or less than 90 with respect to the phase of said voltages of said first phase, and neutralizing reactances for neutralizing the capacity in the tubes between the electron flow control electrodes and the electron receiving electrodes.

19. In a signalling system, a reactance across which alternating voltage appears of a frequency determined by the value of the reactance, a pair of reactance tubes each having a cathode and two electrodes including a control electrode coupled to the said reactance to derive therefrom voltages of the generated frequency substantially in phase quadrature on the said two electrodes of each tube whereby a reactive eifect is provided in each reactive tube, connections between the reactance tubes and the first named reactance to supplement the same by the said provided reactive effects, direct current biasing circuits and a source of direct current potential connected with the electrodes of said tubes and a high resistance in the direct current circuit between the cathode and another electrode in each tube for causing direct current degeneration in said circuits, and means for controlling the gain of the tubes to correspondingly control the provided reactive effects.

20. In a signalling system, an inductive reactance wherein oscillating voltages determined by the value of the reactance appear, two reactance tubes each having two electrodes coupled to the first mentioned reactance to derive therefrom voltages of the generated frequency substantially in phase quadrature whereby a reactive effect is provided in each of said reactance tubes, connections between the reactance tubes and the first mentioned reactance to supplement said first mentioned reactance by the reactances provided in said tubes, and a neutralizing reactance coupling a point on said first mentioned reactance to an electrode in each of said tubes to compensate the reactance coupling within each of said tubes between said two electrodes.

21. In a modulation system an oscillation generator comprising an electron discharge device having an anode, a cathode and a control grid, a circuit including an inductance regeneratively coupling the electrodes of said device for the production of oscillatory energy when direct current operating potentials are applied to the electrodes of said device, direct current connections to said electrodes for applying operating potential thereto including positive direct current for said anode, a reactance tube having two electrodes coupled to said generator to derive therefrom voltages of the generated frequency substantially in phase quadrature whereby a reactive eifect is provided in said reactance tube, connections between the reactance tube and the generating circuit to add said reactive efiect to said circuit to determine in part the frequency of the oscillations generated, means for controlling the gain of the tube in accordance with signals to correspondingly control the value of the reactive efiect and swing the frequency of the oscillations generated, and a resistance and condenser in parallel in the direct current connections to said anode of said device for reducing the said anode voltage to increase said reactive effect and said frequency swing.

22. In apparatus of the nature described, a tuned inductance enclosed in a shield member, means for setting up oscillatory energy of the frequency to which said inductance is tuned in and a control grid, a connection tying the anodes of said devices together and to a terminal of said tuned inductance, a connection between the cathodes of said devices and a point on said inductance, a circuit comprising an inductance tuned to the frequency of the oscillations generated coupling the control grids of said devices in pushpull relation, there being mutual inductance between said last named inductance and said first named inductance, and an electrostatic shield between said inductances.

NATHANIEL I. KORMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,250,095 Crosby July 22, 1941 2,248,132 Smith July 8, 1941 2,250,104 Morrison July 22, 1941 2,278,063 DeLange Mar. 31, 1942 2,351,463 Usselman June 13, 1944 

